The invention relates to a soil sampler, as well as to a method for taking soil samples.
Soil samples are taken at a desired depth by means of a sampling tube, which is vibrated, screwed, driven, etc. into the ground by means of a drill string attached to the upper end thereof, until the desired depth is reached. The distal end (the lower end) of the sampling tube is provided with a valve, such as a cone, that is coupled to the sampling tube and closes a receiving space for the soil. An aid, such as a gripper, is lowered from above through the hollow drill string to receive the soil sample, with the coupling between the valve and the sampling tube disconnected. Subsequently, the drill string including the sampling tube is pressed deeper into the ground with room being made for the soil in the receiving space because the soil stops the valve with respect to the sampling tube.
Mechanical means such as balls, springs and pawls are used for coupling/uncoupling of the valve to/from the sampling tube. In actual practice, however, action of the mechanical means may quickly be impeded by soil particles.
An object of the invention is to overcome the above problem.
A further object of the invention is to provide a soil sampler that is simple in construction and is capable of working reliably over the long term.
Another further object of the invention is to provide a soil sampler that is well-suited for taking soil samples in a layer below a layer of granular material.
The present invention provides a soil sampler comprising a sampling tube having a receiving space for receiving a soil sample, the receiving space being limited in a radial direction by a wall, being open in a distal direction for permitting soil to enter and in a proximal direction being limited by a transverse wall, the transverse wall having line means for supplying and discharging fluid to the receiving space and with means for closing the line means, a free plug or piston being placed in the receiving space closely fitting in there and moveable between the transverse wall and the distal area of the sampling tube and the transverse wall and the plug or piston defining a sealed chamber for fluid when the plug or piston is situated at a distance from the transverse wall.
Thus, use is made of an incompressible fluid body for stopping the soil during movement of the end of the sampling tube to the wanted starting level. To permit entry of the soil, the fluid is permitted to escape via the line means. Mechanical provisions at the distal end of the sampling tube are not required. Long-term reliable action is guaranteed. The plug or piston has the same function as the known cone, but is freely slidable within the receiving space, without connection means to the sampling tube. When sampling occurs through one or several layers of material, particularly granular material, the receiving space can remain closed until the starting level for taking the soil sample has been reached.
Preferably, the plug or piston has a distal surface that is a part of the front surface of the soil sampler. The distal surface has a conical distal surface when the consistency of one or more of the soil layers necessitate a pointed-shaped end for penetration therein.
Preferably, the plug or piston is provided with a cavity in at least one of its axially oriented surfaces. The press force against the radial boundary of the receiving space and thus sealing against fluid leakage as well as against passage of soil material past the plug or piston are improved.
Optimization of the sealing against fluid leakage is obtained when the plug or piston at the proximal side is in liquid-sealing engagement with the wall surface of the receiving space according to a line shaped contact.
A comparable measure can be taken at the distal side of the plug or piston for counteracting soil leakage.
Preferably, the plug or piston has a diabolo-like or hourglass shape.
Preferably, the line means comprise a fluid duct extending through the transverse wall. A valve that can be remotely controlled is present for selectively opening the fluid duct. Preferably, the valve is a one-way valve that is biassed against the distal end of the fluid duct. It is furthermore preferred that the valve comprises a valve disc and a valve rod connected thereto, the valve rod extending through the fluid duct to the proximal side of the transverse wall and being biassed at that location by means of a compression spring. Preferably, the fluid duct is adapted for selective discharge of fluid from the receiving space. When the receiving space is filled with fluid, the valve will prevent escape. When it is desired to let the fluid escape, the valve is operated by pressing against the valve rod by means of a lowered weight, so that the fluid can flow out of the receiving space, corresponding to the volume of the received soil.
Discharge of the fluid can occur via the same duct. It is preferred, however, that the line means comprise a separate and closable supply duct for the fluid.
The supply duct also supplies fluid to the receiving space after raising the soil sampler in order to press out the soil sample.
Preferably, the sampling tube is provided with a core catcher at the distal end to prevent a soil sample of noncohesive material from spilling out after the soil sample has been received.
It may be desirable to pack the soil sample. To that end, according to the invention, means are provided for at least radially enveloping the soil sample received in the receiving space.
In one embodiment, the enveloping means comprise a sleeve arranged at the distal end of the sampling tube such that it can be unwound and extending with a closed end over the open distal end of the receiving space. The sleeve can then be pulled along and unwound by the entering soil.
In case there is a plug or piston, it may be advantageous in the preparation of the soil sampler that the plug or piston is connected to the sleeve.
In an alternative embodiment, a liner is placed in the sampling tube, which liner covers the inner surface of the sampling tube at the location of the receiving space. The liner is already at the desired place prior to the soil sample being taken. It is preferred that a fluid seal is placed between the liner and the sampling tube in order to close off a possible leakage path for the fluid in the receiving space.
Preferably, the plug or piston is in engagement with the inner surface of the liner.
The present invention also provides a method for taking soil samples, wherein a sampling tube having an open end giving access to a receiving space for the soil sample is filled with fluid, is forced into the ground until the location is reached where the soil sample is to be taken, the fluid is given the opportunity to escape while pushing the sampling tube deeper into the ground so that the wanted soil enters the receiving space.
The invention thus provides a method wherein the fluid filled receiving space is sealed to the outside with a fluid sealing free piston, wherein the soil moves the piston to the inside while urging the fluid out when the soil enters.
After disconnecting the cone in known soil samples, soil samples can only be taken from the same location. One or several of the preferred constructions according to the invention discussed above, however, permit closing of the receiving space again at any wanted moment, so that any remaining fluid and the soil already received forms a sealing at the distal end of the sampling tube.
To that end, the invention provides that the receiving space is only partially filled with soil, the fluid is stopped again from escaping, the sampling tube is urged further into the ground to a lower spaced apart desired location, the fluid is given another opportunity to escape while pushing the sampling tube deeper into the ground so that the wanted soil enters the receiving space.
After the soil sampler has been raised, the receiving space is preferably filled with a pressurized fluid to urge the soil sample out of the sampling tube.